Fluids based on fluorocarbon compounds are widely used in many industrial devices, in particular air conditioning, heat pump or refrigeration devices. A feature that these devices have in common is that they are based on a thermodynamic cycle comprising the evaporation of the fluid at low pressure (in which the fluid absorbs heat); the compression of the evaporated fluid up to a high pressure; the condensation of the evaporated fluid to give a liquid at high pressure (in which the fluid discharges heat); and the reduction in pressure of the fluid to complete the cycle.
The choice of a heat-transfer fluid (which can be a pure compound or a mixture of compounds) is dictated, on the one hand, by the thermodynamic properties of the fluid and, on the other hand, by additional constraints. Thus, a particularly important criterion is that of the impact on the environment of the fluid under consideration. In particular, chlorinated compounds (chlorofluorocarbons and hydrochlorofluorocarbons) exhibit the disadvantage of damaging the ozone layer. Thus, henceforth, nonchlorinated compounds, such as hydrofluorocarbons, fluoroethers and fluoroolefins, are generally preferred to them.
The existing heat-transfer devices include in particular high-temperature heat pumps (that is to say, heat pumps with a condensation temperature of greater than or equal to 70° C., indeed even of greater than or equal to 80° C.). These devices are of use in particular in industry, for giving added value to hot streams.
However, high-temperature heat pumps present particular design problems.
This is because the temperature and pressure constraints in the systems of this type are such that few fluids can be used. Thus, fluids such as HFC-134a, which are used for heat transfer in other applications, are not suitable as they exhibit critical temperatures lower than the condensation temperature and thus have very poor performances for high-temperature heat transfer.
The heat-transfer compound conventionally used for high-temperature heat pumps was CFC-114 (dichlorofluoroethane). This compound has to be replaced due to its impact on the environment.
The document U.S. Pat. No. 6,814,884 describes the use of 1,1,1,3,3-pentafluorobutane (HFC-365mfc) in combination with at least one additional compound chosen from 1,1,1,2-tetrafluoroethane (HFC-134a), pentafluoroethane (HFC-125), 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). The HFC-365mfc is present at a level of 40 to 95% by weight and the additional compound at a level of 5 to 60% by weight. A concrete example is provided with 75% of HFC-365mfc and 25% of HFC-227ea, by weight.
Furthermore, the document US 2009/0049856 describes the use of ternary mixtures for high-temperature heat transfer. These ternary mixtures comprise 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) and 1,1,1,3,3-pentafluoropropane (HFC-245fa).
However, the heat-transfer fluids provided in the state of the art for high-temperature heat pumps are still insufficiently effective.
There thus exists a real need to find a heat-transfer fluid which makes it possible to carry out more effective high-temperature heat transfer than the heat-transfer fluids in the state of the art (and which makes it possible in particular to devise high-temperature heat pumps which are more efficient than those of the state of the art), while limiting the negative impact on the environment.